Hybrid vehicle

ABSTRACT

A hybrid vehicle is disclosed, in which the drive torque is controlled according to a target, and the engine operating point and the battery charging rate are controlled thereby as targeted to improve the fuel consumption rate of the hybrid vehicle as a whole An engine torque estimating unit estimates the engine torque based on the motor current, and an engine output correction unit.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a hybrid vehicle having anengine and a motor, or in particular to a hybrid vehicle in which thefuel consumption can be improved by controlling the operating point ofthe engine and the battery charging rate according to a target.

[0002] One system intended to reduce engine fuel consumption is a hybridvehicle utilizing the driving force of the motor. Various types of sucha system have been proposed and include the series type and the paralleltype. For example, JP-A-7-135701 discloses a system in which two motorsand one planetary gear are used so that the engine driving force isinput to the planetary gear, and the motor is controlled to drive thevehicle by the driving force obtained from the output shaft of theplanetary gear. Part of the energy of the engine is derived from agenerator (which is one of the motors) generating power while the motorcoupled to the output shaft of the generator delivers a driving force asan assistance. Thus, the engine is always driven efficiently in a hightorque area while at the same time providing the shift function.

[0003] A method of controlling the driving torque of the hybrid vehicleis described in JP-A-8-207601 in which the torque of the generator iscalculated and the torque of the motor on the output shaft is correctedby the calculated torque of the generator. According to this method, thevehicle driving torque is not affected greatly by variations in theengine output and therefore the drivability can be improved.

[0004] In order to suppress the change in the charging condition of thebattery connected to the generator or the motor, on the other hand,JP-A-10-243503 discloses a method in which the motor torque command orthe target engine speed is corrected in accordance with the currentvalue of the battery. This method can maintain the normal condition ofthe battery and therefore can prevent the deterioration of the battery.Also, the battery charging rate can be controlled as scheduled.

[0005] Of all the methods described above, the method of correcting theoutput of the motor according to the estimated torque value can controlthe vehicle drive torque as intended and therefore can improve thedrivability. Nevertheless, the change in motor output may causeunexpected charge and discharge of the battery, often leading to thedeviation from the optimum schedule for charging the battery, resultingin a deteriorated fuel consumption rate.

[0006] According to the method of correcting the motor output or thetarget engine speed in accordance with the battery current or the like,on the other hand, the battery deterioration can be prevented and theoptimum schedule can be followed. However, the required driving outputcannot be produced often adversely affecting the drivability.

[0007] In any of the methods described above, the engine operatingpoint, if deviated from the target, is not corrected, thereby posing theproblem that the engine deviates from the optimum operating point andthe fuel consumption rate is deteriorated.

SUMMARY OF THE INVENTION

[0008] The object of the invention is to provide a hybrid vehicle nwhich the efficiency and the fuel consumption can be improved bycontrolling the engine operating point and the battery charging rate asintended without adversely affecting the drivability.

[0009] In order to achieve the aforementioned object, according to theinvention, there is provided a hybrid vehicle comprising an engine forgenerating the energy for driving the vehicle, a transmission fortransmitting the driving force to the wheels by changing the rotationalspeed of the engine, at least a motor for changing the wheel drivingforce, a battery for supplying power to the motor, and a drive controlunit for calculating and outputting an operation command value for theengine and the motor based on the drive information including theaccelerator angle, wherein the drive control unit includes an engineoutput correcting mechanism for correcting the operation command valuefor the engine based on the difference between the engine operationcommand value and the torque generated by the engine thereby to maintainan optimum engine operating point.

[0010] The optimum operating point is defined as a point on or near acurve associated with the best fuel consumption rate of the engineincluding the efficiency of the transmission and the motor.

[0011] According to another aspect of the invention, there is provided ahybrid vehicle comprising an engine for generating the energy fordriving the vehicle, a transmission for transmitting the driving forceto the wheels by changing the rotational speed of the engine, at least amotor for changing the wheel driving force, a battery for supplyingpower to the motor, means for determining a target engine torque, meansfor calculating the torque generated by the engine, and means forcorrecting the engine output based on the difference between the targetengine torque value and the engine torque value calculated by the enginetorque calculation means.

[0012] According to still another aspect of the invention, there isprovided a hybrid vehicle comprising an engine for generating the energyfor driving the vehicle, transmission for transmitting the driving forceto the wheels by changing the rotational speed of the engine, at least amotor for changing the wheel driving force, a battery for supplyingpower to the motor, means for determining a target engine output valueinstead of the engine torque, means for calculating the output of theengine, and means for correcting the engine output based on thedifference between the target engine output value and the calculatedengine output value.

[0013] According to yet another aspect of the invention, there isprovided a hybrid vehicle comprising an engine for generating the energyfor driving the vehicle, a transmission for transmitting the drivingforce to the wheels by changing the rotational speed of the engine, atleast a motor for changing the wheel driving force, a battery forsupplying power to the motor, a battery management unit for determininga target current value of the battery, means for detecting the batterycurrent, and means for correcting the engine output based on thedifference between a target battery current and a detected batterycurrent value, wherein the battery management unit produces a schedulefor the battery charging rate based on the navigation information anddetermines the target battery current value based on the differencebetween the detected value of the battery charging rate and thescheduled battery charging rate.

[0014] The engine output correcting means can correct the output bycontrolling the throttle opening degree or correcting the target engineoutput value.

[0015] According to this invention, an optimum engine operating pointcan be maintained while producing the target vehicle driving torque andalso the battery charging rate can be kept as scheduled for an improvedfuel consumption rate.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a diagram showing an example of a configuration of adriving system of a hybrid vehicle according to this invention.

[0017]FIG. 2 is a diagram showing a configuration of a drive controlunit shown in FIG. 1.

[0018]FIG. 3 is a diagram showing a configuration of an engine outputcorrecting unit shown in FIG. 2.

[0019]FIG. 4 is a diagram for explaining the engine operating point.

[0020]FIG. 5 is a diagram showing a configuration of another example ofthe hybrid vehicle driving system according to this invention.

[0021]FIG. 6 is a diagram showing a configuration of the drive controlunit shown in FIG. 5.

[0022]FIG. 7 is a diagram showing another configuration of the drivecontrol unit of the hybrid vehicle driving system according to theinvention.

[0023]FIG. 8 is a diagram showing still another configuration of thedrive control unit according to this invention.

[0024]FIG. 9 is a diagram showing a configuration of the hybrid vehicleof another type according to the invention.

[0025]FIG. 10 is a diagram showing yet another configuration of thedrive control unit according to the invention.

DESCRIPTION OF THE EMBODIMENTS

[0026]FIG. 1 shows a hybrid vehicle in which the tires 3 a, 3 b arerotated by use of the energy of an engine through a drive shaft 2. Thishybrid vehicle including a planetary gear train A4 and a planetary geartrain B5 as a differential mechanism each including a sun gear, aplanetary gear and a ring gear. The sun gears are driven by a motor A8and a motor B9 controlled by power converters 10, 11, respectively. Thebattery 12 is used for supplying the energy required by these motors orstoring the energy generated in these motors at the time of decelerationbraking. Each planetary gear is fastened to the same input shaft, andthe driving torque of the engine 1 is divided into two or more planetarygears. The ring gears, on the other hand, are coupled to a common outputshaft through gears having different gear ratios. The torque output fromthe two planetary gear trains are combined into a vehicle drive torqueτv. As a result, it is possible to secure an acceleration ordeceleration of the vehicle as intended by the driver. By controllingthe torque τa, τb and the speeds ωa, ωb of the motors A8, B9 for drivingthe sun gears, on the other hand, the vehicle drive torque τv and theengine speed ωe can be regulated. The drive control unit 31 calculatesand outputs the engine throttle opening degree command value θt, thespeed command value ωar of the motor A and the torque command value τbrof the motor B using predetermined functions and data according topredetermined processing steps based on the information including theaccelerator angle θa, the vehicle speed ωv, the torque command value τarof the motor A and the currents Ia, Ib of the motors A, B. The drivecontrol unit 31 is configured with a microcomputer including a CPU, aRAM, a ROM, input/output control means and various programs stored inthe ROM.

[0027] A specific method of controlling the motors A8, B9 is describedbelow. In the system shown in FIG. 1, equations (1) to (4) below hold.

ωe=Kpωa+Kaωv  (1)

ωe=Kpωb+Kbωv  (2)

τe=(τa+τb)/Kp  (3)

τv=(Kaτa+Kbτb)/Kp  (4)

[0028] where ωe, ωv, ωa, ωb are the engine speed, the vehicle speed, therotational speed of the motor A and the rotational speed of the motor B,respectively, and τe, τa, τb, τv the engine torque, the torque of themotor A, the torque of the motor B and the vehicle drive torque,respectively. Characters Kp, Ka, Kb are constants relating to the gearratio.

[0029] Using this relation, the following equation (5) is obtained fromequation (1).

ωar=(ωer−Kaωv)  (5)

[0030] where ωer is the target engine speed, ωv the detected vehiclespeed and ωar the rotational speed setting of the motor A.

[0031] By controlling the rotational speed of the motor A based on thisequation, the engine can be driven at the desired operating point andthe desired change gear ratio is obtained.

[0032] Also, let τvr be the target vehicle drive torque, and τa be theoutput torque of the motor A, and from equation (4), the followingrelation holds.

τbr=(Kpτvr−Kaτa)/Kb  (6)

[0033] Assuming that τbr determined from equation (6) is a torquesetting of the motor A, the desired vehicle drive torque can beobtained.

[0034] By controlling the motors according to equations (5) and (6), theengine speed can be controlled to the desired change gear ratio or thetarget vehicle drive torque can be generated. Equation (6) contains noengine torque τ e, and therefore even when the engine torque undergoes achange, the vehicle drive torque can be controlled as targeted bycontrolling the two motors.

[0035] The drive control unit 31, which is for realizing theaforementioned control operation, calculates and outputs the enginethrottle opening command value θt, the speed command value ωar of themotor A and the torque command value τbr of the motor B based on theinformation including the accelerator angle θa, the vehicle speed ωv,the torque command value τar of the motor A and the currents Ia, Ib ofthe motors A, B. The throttle opening command value θt is sent to thethrottle control unit 13, the motor A speed command value ωar to themotor A control unit 14, and the motor B torque command value τbr to themotor B control unit 15 thereby to actually control the engine and themotors.

[0036] The motor A control unit 14, based on the difference between thespeed command value ωar and the speed detection value ωa, produces thetorque command value τar in such a manner as to eliminate the differenceby the proportional integral control or the like thereby to control thepower converter 10. Also, the torque command value τar involved is sentto the drive control unit 31.

[0037] Now, the configuration of the drive control unit 31 will beexplained with reference to FIG. 2.

[0038] First, the target drive torque determining unit 21 determines atarget drive torque τvr of the vehicle based on a map predetermined fromthe accelerator angle θa and the vehicle speed ωv.

[0039] In the overall control unit 22, the engine output and the changegear ratio are determined based on the target drive torque τvr and thevehicle speed ωv, and the engine operating point X (the target enginespeed ωer, the target torque τer) is calculated. In the process, theoperating point is determined in such a manner as to enable the engineto operate in an area as efficient as possible.

[0040] The engine control unit 23 determines the throttle openingcommand value θto in accordance with the target engine speed ωer and thetarget torque τer determined in the overall control unit 22. Thecorrection value Δθt determined in the engine output correction unit 27is added to θto to obtain θt, and a command is issued to the throttlecontrol unit 13.

[0041] The motor A control unit 24 calculates the speed command valueωar determined in equation (5) based on the target engine speed ωerdetermined in the overall control unit 22 and the actual measurement ωvof the vehicle speed and issues a speed command to the motor A controlunit 14.

[0042] The motor B control unit 25 calculates the torque command valueτbr of the motor B by substituting τar into τa of equation (6) based onthe target drive torque τvr of the vehicle and the torque command valueτar of the motor A8 sent from the overall control unit 22, and issues acommand to the motor B control unit 15.

[0043] The engine torque estimation unit 41 determines an estimatedengine torque τe by the following method from the armature currents Ia,Ib of the motors A8, B9.

[0044] First, the input torque τai of the motor A8 is calculated basedon the following equation from the armature current Ia of the motor A8.

τai =PnθIq+Pn(Ld−Lq)IdIq   (7)

[0045] where θ is the magnetic fluxes interlinking the armature, Pn thenumber of poles, Id, Iq the Ia components along d and q axes,respectively, and Ld, Lq inductances of the armature winding along d andq axes, respectively.

[0046] Then, the output torque τa is calculated from the relation ofequation (8)

τa=τai−Ja(dωa/dt)  (8)

[0047] where Ja is the inertia of the motor A8, and dωa/dt the changerate of the rotational speed. The change rate of the rotational speedcan be calculated from the difference of the rotational speed ωa or thelike. A simple method of this calculation is to ignore the term of thechange rate of the rotational speed and regard the input torque as anoutput torque.

[0048] This is also the case with the motor B, for which the outputtorque τb is calculated from the armature current Ib. The motor outputtorque τa and τb thus calculated are substituted into equation (3)thereby to determine the estimated engine torque τe.

[0049] The engine output correction unit 42 calculates the throttleopening correction value Δθt in accordance with the difference betweenthe target engine torque τer and the estimated engine torque τe. Thecorrection value is determined in such a manner as to increase thethrottle opening in the case where the estimated torque is smaller, andto decrease the throttle opening in the case where the estimated torqueis larger. By doing so, the engine output can be controlled so that theengine torque approaches the target torque.

[0050]FIG. 3 shows an example configuration for the proportionalintegral control. By setting the gains Kp and Ki appropriately, thecontrol operation can be performed to eliminate the difference betweenthe target torque and the estimated torque rapidly.

[0051] Now, the effect of correcting the engine output will be explainedwith reference to FIG. 4. Assume that the overall control unit 22 hasdetermined a target operating point of the engine at point X on the bestfuel consumption curve including the transmission efficiency and themotor efficiency based on a given target drive torque τvr and thevehicle speed ωv. The engine control unit 23 controls the throttle valveto attain the operating point at point X. In view of the fact that theengine characteristics change with the atmospheric pressure or the like,however, the target output may fail to be achieved. For example, theactual torque may deviate to point Y. By the way, the engine speed ωe,which can be controlled accurately by controlling the speed of the motorA, is assumed not to develop any deviation.

[0052] Once the actual operating point deviates from the targetoperating point in this way, the optimum operating point is missed, andtherefore the fuel consumption rate may deteriorate. Also, the controlmethod described above is intended to secure the required drive torquefrom the motor regardless of the engine torque, and therefore the engineoutput deviation from the target leads to an unexpected discharge orcharge of the battery power. In the case of FIG. 4, for example, theengine output runs short and therefore the motor output increasescorrespondingly, resulting in the battery being discharged. A protractedsituation of this battery discharge will cause the battery charging rateto deviate from the target value and therefore the need arises for anunexpected charging operation, thereby leading to an overalldeterioration of the efficiency.

[0053] The present invention is intended for a control operation inwhich the target engine operating point is set at or in the vicinity ofpoint X (optimum operating point) on the total best fuel consumptionrate curve including the efficiency of the transmission and the motor.The use of this method can correct this engine torque deviation andrestore the operating point at or in the vicinity of point X. Thus, theengine operates at the optimum operating point and the battery chargingrate undergoes no unexpected change, thereby preventing thedeterioration of the fuel consumption rate.

[0054] In the aforementioned example, the output torque is calculatedfrom the armature current of the motor. As an alternative, an estimatedengine torque value τe can be determined by substituting the torquecommand values τar, τbr directly into τa, τb in equation (3). In such acase, the estimation is possible using a simple method without using themotor current at the sacrifice of the likelihood of an estimation errorbeing developed.

[0055] A similar effect is attained also by attaching a torque detectorto the engine output shaft and using the output of the torque detectoras an estimated torque value. In such a case, the detection accuracy isimproved as compared with the estimation based on the motor torque.

[0056] Also, instead of correcting the output based on the deviationfrom the target engine torque value as in the aforementioned case, asimilar effect can be obtained by a method of detecting the deviationfrom the target engine output. The engine output is determined as theproduct of the engine torque and the engine speed. In FIG. 2, therefore,this method can be accomplished by adding the engine speed information.

[0057] Now, another example configuration of the drive control unit willbe explained with reference to FIGS. 5 and 6. In this example, thedistance to be covered up to the destination constituting the navigationinformation, the current Ic flowing in the battery 12 and the batterycharging rate SOC are input to the drive control unit 32.

[0058] The battery management unit 43 first produces a schedule for thebattery charging rate based on the navigation information. In the casewhere a mountainous road and an ascending slope are in the way ahead,the battery charging rate is set to a larger value to provide asufficient torque assistance by the motor. In the case where adescending road ahead is forecast, on the contrary, the battery chargingrate is set to a smaller value to provide a sufficient regenerativebraking. Also, in the case where an urban area is nearing and alow-speed run on the motor is expected, the battery charging rate isincreased.

[0059] Then, the battery charging rate schedule thus prepared iscompared with the current battery charging rate, and based on thedifference, a target power value Pcr to be charged to (or dischargedfrom) the battery is determined. At the same time, the target value Icrof the charge (or discharge) current for the battery is calculated. Thetarget battery current value Icr is calculated by solving the quadraticequation (9), for example.

Pcr=IcVo+Ic²R  (9)

[0060] where vo is the electromotive force of the battery, and R theinternal resistance of the battery. As for the signs attached to Pcr andIcr, the plus sign is defined as indicating the charging and the minussign as indicating the discharge.

[0061] The overall control unit 22 determines the engine output and thechange gear ratio based on the target drive torque τvr, the vehiclespeed ωv and the target battery power Pcr, and calculates the engineoperating point (target engine speed ωer, the target engine torque τer).In the case where the target battery power value Pcr is positive(charging), the target engine output value is the sum of the output fordriving the vehicle and the output for charging the battery. In the casewhere the target value Pcr is negative (discharge), on the other hand,the target engine output is decreased correspondingly.

[0062] As described above, by correcting the target engine output valueas required for the charge or discharge of the battery, the batterycharging rate can be managed as targeted. In view of the aforementionedfact that the engine characteristics are subjected to various changes,however, the target output is not always produced. In the case where thetarget X is missed and the point Y is reached instead, as shown in FIG.4, for example, the engine output decreases and the discharge increasescorrespondingly. Also, the loss occurring in the motor may changedepending on the prevailing conditions. As a result, it may be that thetarget battery current cannot be secured, often making it impossible tomanage the battery charging rate to the target value. In such a case,the correction is carried out by the engine output correction unit 44 asdescribed below.

[0063] In the engine output correction unit 44, the throttle openingcorrection value Δθt is calculated based on the difference between thetarget battery current value Icr and the detected current value Ic. Inthe case where the detected value is smaller, the throttle valve openingis increased to increasing the charging rate, while in the case wherethe detected value is larger, the throttle opening value is reduced. Asa result, the engine operating point is corrected from point Y to pointX, for example, in FIG. 4 thereby making it possible to control thebattery current toward the target value. As a configuration of thecontrol system, the proportional integral control similar to that shownin FIG. 3 can be used. By doing so, the engine output, even if itdeviates from the target value, can be corrected so that the batterycurrent attains the target value.

[0064] Now, another configuration example of the drive control unit 32will be explained with reference to FIG. 7. In this example, the engineoutput correction unit 45 outputs the battery power correction valueθPcr but not the throttle opening correction value Δθt based on thedifference between the target battery current value Icr and the detectedbattery current value Ic, and adds the battery power correction valueΔPcr to the target battery power value Pcr output from the batterymanagement unit. In the case where the detected battery current value issmaller than the target battery current value, the target battery powervalue is corrected upward. By doing so, the target engine output valueis corrected and therefore the engine output is indirectly corrected,thereby making it possible to control the battery current as targeted.

[0065] Further, an example configuration with the cases of FIGS. 2 and 7combined is shown in FIG. 8. In this case, the engine output correctionunit 42 outputs the throttle opening correction value Δθt based on theestimated engine torque value, and the engine output correction unit 45outputs the battery power correction value ΔPcr based on the detectedbattery current value. With this configuration, the engine is alwayskept at the optimum operating point, while at the same time controllingthe battery current to the target value.

[0066] The foregoing description concerns the case in which the schedulefor battery charging rate is prepared by the battery management unit 43using the navigation information. The present invention is applicable,however, also to the case where the charging rate is managed simply bysetting the upper and lower limits thereof without using the navigationinformation. In such a case, too, the battery charge and discharge canbe controlled to the target by correcting the engine output while alwayssecuring the vehicle driving force.

[0067] Now, an explanation will be given of the case in which theinvention is applied to an ordinary hybrid vehicle other than shown inFIG. 1.

[0068]FIG. 9 shows a hybrid vehicle comprising an engine 1, atransmission 17, a motor 16 for changing the drive torque, and a powerconverter 11 and a battery 12 for driving the motor. The drive controlunit 30 outputs the engine throttle opening command value θt, the changegear ratio command value r, the motor torque command value τr based onthe information including the accelerator angle θa and the vehicle speedωv. The throttle opening command value θt is sent to the throttlecontrol unit 13, the change gear ratio command r to the transmissioncontrol unit 19, and the motor torque command τr to the motor controlunit 15.

[0069] The configuration of the drive control unit 34 will be explainedwith reference to FIG. 10. The target torque determining unit 21, theoverall control unit 22, the engine control unit 23 and the batterymanagement unit 43 are similar to the corresponding parts shown in FIG.6. The transmission control unit 27 calculates the change gear ratiocommand value r from the target engine speed ωer determined by theoverall control unit 22 and the actual measurement ωv of the vehiclespeed, and issues a command to the transmission control unit 19. Themotor control unit 26 calculates the torque required of the motor forassistance, from the target drive torque τvr of the vehicle and thetarget engine torque τer, and outputs a motor torque command τr.

[0070] The engine output correction unit 44 operates similarly to thecase of FIG. 6 and calculates the throttle opening correction value Δθtbased on the difference between the target battery current value Icr andthe detected battery current value Ic output from the battery managementunit 43. In the case where the detected value is smaller, the throttleopening value is increased to increase the charging rate, while in thecase where the detected value is larger, the throttle opening isdecreased. As a result, the battery current can be controlled toapproach the target value.

[0071] There is also a method for correcting the battery current whichmay be different from the target value in response to a command from themotor. This method, however, employed is at the risk of failing toachieve the target drive torque of the vehicle. In this method, if themotor is controlled to produce the target drive torque and the batterycurrent is corrected on the engine side, the battery charging rate canbe managed while at the same time producing a target drive torque.

[0072] It will thus be understood from the foregoing description thataccording to this invention, the engine output is corrected whilemaintaining a target vehicle driving force, thereby making it possibleto control the engine operating point and the battery charging rate tothe target, thereby improving the fuel consumption rate of the vehicleas a whole.

What is claimed is:
 1. A hybrid vehicle comprising: an engine forgenerating the energy for driving the vehicle; a transmission forchanging the engine speed and transmitting the driving force to thewheels; at least a motor for increasing/decreasing the wheel drivingforce; a battery for supplying power to said motor; and a drive controlunit for calculating and outputting an operation command for said engineand said motor based on the operation information including theaccelerator angle; wherein said drive control unit includes an engineoutput correction mechanism for correcting the operation command valuefor said engine and maintaining an optimum operating point of saidengine.
 2. A hybrid vehicle comprising: an engine for generating theenergy for driving the vehicle; a transmission for changing the enginespeed and transmitting the driving force to the wheels; a motor forincreasing/decreasing the wheel driving force; a battery for supplyingpower to said motor; means for determining a target torque value of saidengine; means for calculating the engine torque generated by saidengine; and means for correcting the output of said engine based on thedifference between the target value of the engine torque and the enginetorque calculated by said engine torque calculation means.
 3. A hybridvehicle according to claim 1 , wherein the torque generated by saidengine is calculated based on the detected torque value of said motor ora toque command value.
 4. A hybrid vehicle according to claim 2 ,wherein said torque generated by said engine is calculated based on thedetected torque value of said motor or a torque command value.
 5. Ahybrid vehicle comprising: an engine for generating the energy fordriving the vehicle; a transmission for changing the engine speed andtransmitting the driving force to the wheels; a motor forincreasing/decreasing the wheel driving force; means for determining atarget output value of said engine; means for calculating the outputgenerated by said engine; and means for correcting the output of saidengine based on the difference between the target engine output valueand the engine output value calculated by said engine output calculationmeans, thereby maintaining an optimum operating point of said engine.